1. Field of the Invention
The present invention relates in general to an apparatus for controlling an automotive vehicle, more specifically, an engine, an automatic transmission and other devices of the vehicle. More particularly, the present invention is concerned with means for preventing an interference between running stability control means and controls of various devices in power transmitting system of the vehicle.
2. Discussion of the Related Art
An automotive vehicle may fall in an unstable running condition, in particular, an unstable turning condition, with the lateral road gripping capacity of a wheel tire being exceeded during turning of the vehicle on a road surface having a relatively low friction coefficient, or at a relatively high speed, or to clear an obstacle, for example. The unstable running condition may be an oversteering or understeering tendency of the vehicle. The oversteering tendency is caused when the road gripping force of the rear wheels is considerably smaller than that of the front wheels, resulting in an excessively larger turning angle of the vehicle than the steering angle, and leading to a spinning tendency of the vehicle. On the other hand, the understeering tendency is caused when the road gripping force of the front wheels is considerably smaller than that of the rear wheels, resulting in a considerably smaller turning angle of the vehicle than the steering angle.
To cope with such running instability of the vehicle, there has been proposed a turning stability control apparatus for stabilizing the vehicle turning behavior, such as a vehicle stability control system (VSC system) as disclosed in JP-A-4-266538. Such a turning stability control apparatus is activated when the vehicle turning condition is unstable, namely, when an oversteering or understeering tendency of the vehicle is detected. Described in detail, the apparatus is adapted to reduce the engine output and at the same time apply a braking force to an appropriate one or ones of the front and rear wheels, for producing a moment that reduces the oversteering or understeering tendency of the vehicle, thereby to stabilize the turning behavior of the vehicle.
In the automotive vehicle equipped with such a turning stability control apparatus, there are encountered various sorts of drawbacks due to interferences or inadequate coordination between an operation of the turning stability control apparatus, and an operation of a shift control device for shifting an automatic transmission of the vehicle.
For instance, such drawbacks may arise when a shift-down action of the automatic transmission takes place while the vehicle drive force is reduced by reducing the opening angle of a throttle valve or while at least one of the vehicle wheels is braked by a braking system, for improving the turning stability of the vehicle. The turning stability control apparatus may be operated during running of the vehicle on a road surface having a low friction coefficient, for example. In this case, the drive wheels of the vehicle may slip on the road surface having a low friction coefficient, due to an engine braking effect provided by the shift-down action of the automatic transmission. As a result, the turning stability control by reduction of the vehicle drive force or brake application may be deteriorated due to the slipping of the drive wheels caused by the shift-down action of the automatic transmission.